This is an example of retroactive naming: Giner named himself after the planet's name rather than the converse.

As for Bucan, I suspect that he too named himself after the planet.

The other explanation:
1. Planet names are strings of two or more words. 'Bucan' is a possible combination.
2. The chance of 'Bucan' appearing is very small, say 1 in a million. Presume 1000 prefixes and 1000 suffixes in Kosmor's generator.
3. P(Not 'Bucan') = 1 - 1/(10^6)

Probability of one 'Bucan' in the observed galaxy = 1 - (1 - 1/(10^6))^n
Where n is the number of observable planets. Agnari can see about 10^4 planets, so we can use this as an estimate.

Therefore: P(One observable 'Bucan') = 0.995 %. Possible, but small.
If we count everyone else, the number of observed systems probably increases by a magnitude, and the probability of an observed 'Bucan' is then 9.52%.

The probability calculation is based on the approximate number of observed planets. Go to mapshare, select a swathe of your map, and it will tell you how many solar systems are in the area (go try it!).

Agnari's maps give a figure in the order of 10^4. Assuming other empires have similar star density, we can extrapolate the true observed figure to be another magnitude greater.

Yes, the above assumes that names may be repeated. However, we have no a priori information that 'Bucan' exists in the non-observable part of the galaxy (duh).

*Hence we cannot use P(Observed 'Bucan' | Unobserved 'Bucan') = 0.

By simple math substitution into the formula, you can convince yourself that forcing names to be unique actually INCREASES the chances of observing a planet named 'Bucan'.

Lastly, the figures are dependent on the lengths of the suffix and prefix lists (that I have assumed). I am trying to explain that 'incredible' coincidences are not as wonderous as they may appear.